Laser scanning techniques for writing or printing on a medium sensitive to the laser beam have been disclosed in the prior art as shown, for example, in U.S. Pat. No. 3,922,485. In general, the laser beam is intensity modulated in accordance with ifnormation to be printed on a receiving medium, the modulated laser beam being directed to a rotating scanner, or reflector, such as a multi-faceted polygon. The rotating scanner in turn causes the modulated laser beam to scan, in sequence, across a sensitive medium located a distance away from the scanner. The information contained in the intensity modulated laser beam can be directly written on the medium if the medium is sensitive to the laser beam, or in an alternative embodiment, the laser beam can selectively discharge a charged insulating or semiconducting surface, such as a photoconductor, in accordance with the intensity of the beam. In the alternative embodiment, the degree of charge dissipation corresponds to the information contained in the intensity of the laser beam. The areas of the medium which are not discharged by the laser beam are subsequently developed, for example, by standard xerographic techniques.
Present day copiers which are commercially available which utilize the xerographic process include a platen upon which the document to be reproduced is placed, the platen being flat or curved. The document is generally flood illuminated or scanned with light and the reflections therefrom are imaged via a copy lens to a charged photoconductive medium to discharge the medium in accordance with the image formed on the document.
The Telecopier.RTM. 200, a facsimile transceiver manufactured by the Xerox Corporation, Stamford, Conn., directs reflections from a laser scanned document onto a photosensitive transducer, the electrical signal output thereof being transmitted to another or remote location and used to modulate a laser beam to reproduce the scanned document. However, the Telecopier 200 is generally not considered a copier type device since, inter alia, a scanning platen and other copier features are not available.
Although copiers now commercially available are not adapted to utilize scanning techniques to scan a document placed on the copier platen line by line to produce a serial bit stream corresponding to the scanned information (i.e. a raster type scanning system), it would be advantageous if such copiers or other reproduction devices available could be modified to incorporate the laser printing technique disclosed, for example, in the aforementioned patent, the modified copier thus requiring a system which provides for two-dimensional input scanning. A system for two-dimensional raster input scanning which utilizes a laser, is described, for example, in U.S. Pat. No. 3,970,359. Copending application Ser. No. 546,478 filed Feb. 3, 1975, now U.S. Pat. No. 4,012,585 and assigned to the assignee of the present invention, provides a flying spot scanning system which is capable of scanning an unmodulated beam to a reading station for reading a stationary document and a modulated beam to an imaging station for, inter alia, reproducing the scanned document thereat.
The availability of a copier or other reproduction device which utilizes two-dimensional input scanning, such as the raster type input scanning of a document placed on a platen as described hereinabove and laser scanning techniques for writing on a laser sensitive medium would provide many advantages inherent with the use of lasers and non-flood illuminating input scanning techniques, such as increased copying speeds and resolution. In particular, it would be advantageous if an intermediate storage medium was provided between the input and output scanning stations (in this regard, the output scanning station may be located at a position remote from the input scanning station) to allow for manipulation and storage of the scanned information, and, in particular, to provide for electronic precollation which electronically arranges representations of images to allow collated sets of documents to be reproduced. Other desirable features of such a copier would include input scan reversal for alternate bound pages during bound volume scanning, synchronization of the system by a clock associated with the storage member, a synchronous system reducing the size and cost of a synchronizing buffer associated therewith, input/output interleaving with a print interrupt feature, image centering and edge fadeout for image reduction, and independent magnification/demagnification by separately variable raster spacing.